Visual Basic 2012 Lesson 6- Managing Data

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Visual Basic programming often involves manipulation of all sorts of data. Among them, some can be calculated while others are in the form of text, date, time and more. Visual Basic 2012 divides data into different types so that it is easier for the programmers to manage them.

6.1 Visual Basic 2012 Data Types

Visual Basic 2012 classifies data into two major data types,  the numeric data type and the non-numeric data type.

6.1.1 Numeric Data Types

Numeric data types are types of data that consist of numbers that can be computed mathematically. Some examples of numeric data types are examination marks, height, weight, the price of goods, monthly bills, fees and etc.

In Visual Basic 2012, numeric data are classified into seven types, depending on the range of values they can store. Calculations that do not require precision can use Integer or the Long integer in the computation. On the other hand, programs that require high precision calculation need to use Single and Double precision data types which also called floating point numbers. In addition, for currency calculation, you can use the currency data types. Lastly, if even more precision is required in performing a calculation, we can use the decimal data types. These data types are summarized in Table 6.1

Table 6.1

Type Storage Range of Values
Byte 1 byte 0 to 255
Integer 2 bytes -32,768 to 32,767
Long 4 bytes -2,147,483,648 to -2,147,483,648
Single 4 bytes -3.402823E+38 to -1.401298E-45 for negative values
1.401298E-45 to 3.402823E+38 for positive values
Double 8 bytes -1.79769313486232E+308 to -4.94065645841247E-324 for negative values
4.94065645841247E-324 to 1.79769313486232E+308 for positive values
Variant(numeric) 16 bytes Any value as large as double
Currency 8 bytes -922,337,203,685,477.5808 to 922,337,203,685,477.5807
Decimal 12 bytes +/-79,228,162,514,264,337,593,543,950,335 if no decimal
+-7.9228162514264337593543950335



6.1.2 Non-numeric Data Types

Non-numeric data types are data that cannot be manipulated mathematically using standard arithmetic operators. These types of data comprise text or string data types, the Date data types, the Boolean data types, the Object data type and the Variant data type. We can summarise the data types as shown in Table 6.2

Table 6.2 Non-numeric Data

Data Type Storage Range of Values
String(fixed length) Length of String 1 to 65,400 characters
String(variable-length) Length +10 bytes 0 to 2 billion characters
Date 8 bytes January 1,100 to December 3,9999
Boolean 2 bytes True or False
Object 4 bytes Any embedded object
Varient(text) Length+22 bytes Same as variable-length string



6.1.3 Suffixes for Literals

Literals are values that you assign to a data. Usually, we  add a suffix behind a literal so that Visual Basic 2012 can handle the calculation more accurately. For example, we can use num=1.3089# for a Double type data. Some of the suffixes are displayed in Table 6.3.

Table 6.3

Suffix Data Type
& Long
! Single
# Double
@ Currency

In addition, we need to enclose string literals within two quotations and we enclose date and time literals within two # sign. Strings can contain any characters, including numbers. The following are few examples:

memberName="Turban, John."
TelNumber="1800-900-888-777"
LastDay=#31-Dec-00#
ExpTime=#12:00 am#

6.2 Managing Variables

A Variable is like a mailbox in the post office as the content of the variable changes every now and then, just like the mailbox.  In Visual Basic 2012, variables are areas allocated by the computer memory to hold data. In addition,  each variable must be given a name. To name a variable in Visual Basic 2012, you have to follow a set of rules.

6.2.1 Variable Names

The following are the rules when naming the variables in Visual Basic 2012

  • It must be less than 255 characters
  • No spacing is allowed
  • It must not begin with a number
  • Period is not permitted

Some examples of valid and invalid variable names are displayed in Table 6.4

Table 6.4

Valid Name Invalid Name
My_Car My.Car
ThisYear 1NewBoy
Long_Name_Can_Be_USED He&HisFather *& Not allowed

6.2.2 Declaring Variables

In Visual Basic 2012, we need to declare a variable by assigning a name and a relevant data type before using it. If you fail to do so, the program may encounter an error.  Usually, we declare the variables in the general section of the code window using the Dim statement. The syntax  to declare a varibale is as follows:

Dim Variable Name As Data Type

Example 6.1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim password As String
Dim yourName As String
Dim firstnum As Integer
Dim secondnum As Integer
Dim total As Integer
Dim doDate As Date
End Sub

You may also combine them in one line, separating each variable with a comma, as follows:

Dim password As String, yourName As String, firstnum As Integer,.............

For string declaration, there are two possible forms, one for the variable-length string and another for the fixed-length string. For the variable-length string, just use the same syntax as example 6.1 above. However, for the fixed-length string, you have to use the syntax  as shown below:

Dim VariableName as String * n, where n defines the number of characters the string can hold.

Example 6.2:

Dim yourName as String * 10

yourName can hold no more than 10 Characters.

6.2.3 Assigning Values to Variables

After declaring various variables using the Dim statements, we can assign values to those variables. The syntax of an assignment is

Variable=Expression

The variable can be a declared variable or a control property value. The expression could be a mathematical expression, a number, a string, a Boolean value (true or false) and etc. The following are some examples:

firstNumber=100
secondNumber=firstNumber-99
userName="John Lyan"
userpass.Text = password
Label1.Visible = True
Command1.Visible = false
Label4.Caption = textbox1.Text
ThirdNumber = Val(usernum1.Text)
total = firstNumber + secondNumber+ThirdNumber

6.3 Constants

Constants are different from variables in the sense that their values do not change during the running of the program.

6.3.1 Declaring a Constant

The syntax to declare a constant is

Const Constant Name As Data Type = Value

Example 6.3

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 Const Pi As Single=3.142
 Const Temp As Single=37
 Const Score As Single=100
End Sub



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